This application is based on and claims priority under 35 U.S.C. xc2xa7119 with respect to a Japanese Patent Application 2001-014073 filed on Jan. 23, 2001, the entire content of which is Incorporated herein by reference.
This invention generally relates to a hydraulic brake apparatus for a vehicle. More particularly, this invention pertains to a vehicle hydraulic brake apparatus adapted to perform auto-braking control regardless of operation of a brake pedal and provided with a master cylinder, an auxiliary hydraulic pressure source, and a regulating mechanism.
Various types of vehicle hydraulic pressure brake apparatus are known. U.S. Pat. No. 5,978,725 (corresponding to a Japanese Patent Application Toku-Kai-Hei 11-157424) discloses a brake control apparatus for switching a control mode from an auto-braking mode in which a brake force is controlled according to the distance between the vehicle and another forwardly located vehicle or obstacle to a manual braking mode in which the brake force is controlled in accordance with the braking operation by a driver. The brake control apparatus disclosed in the U.S. patent mentioned above is designed to decrease a variation of the brake force when the control mode is switched from the auto-braking mode to the manual braking mode in accordance with the braking operation by the driver. To do this, the time at which the auto-braking mode should be switched to the manual braking mode is set to be delayed from the start time of the braking operation.
The patent describes that the disclosed brake control apparatus is intended to overcome drawbacks which may be included in a running control apparatus according to Japanese Patent Laid-Open Publication 4-201629. In this running control apparatus, when a driver carries out a braking operation (a depressing operation of the brake pedal) during the brake force control in the auto-braking mode, the intention of the driver takes priority over the brake force control in the auto-braking mode so that the auto-braking mode is released. As a result, the vehicle is braked with a brake force corresponding to the amount of operation of the brake pedal (in the manual braking mode).
The brake control apparatus disclosed in the above-mentioned U.S. patent can delay the time at which the auto-braking mode should be switched to the manual braking mode so that the auto-braking mode is switched to the manual braking mode in a state where the brake force corresponding to the amount of the braking operation after start of the braking operation has been generated. Therefore, the brake control apparatus can effectively decrease a variation with respect to the brake force when the auto-braking mode is switched to the manual braking mode.
The objective of the brake control apparatus described in the aforementioned U.S. patent and the objective of the running control apparatus described in the aforementioned the Japanese patent publication are similar in that the variation of the brake force should be decreased when the control mode is switched from the auto-braking mode to the manual braking mode. That is, the brake force according to the auto-braking mode is switched to the brake force generated by a master cylinder hydraulic pressure only in response to the brake pedal operation when the control mode is switched from the auto-braking mode to the manual braking mode at a predetermined time.
According to the brake control apparatus with the above-described structure in which the control mode is switched from the auto-braking mode to the manual braking mode at the predetermined time, when the amount of brake pedal operation is small in the situation where the brake pedal operation is performed during the auto-braking mode in response to the driver""s intention to require a further brake force, the brake force may not be generated as sufficiently as the driver expects or desires. Thus, sufficient brake feeling may not be obtained by the driver. For example, when the brake pedal is operated in response to the driver""s intention to require the brake pedal operation in the state where the brake force has been controlled in the auto-braking mode regardless of the brake pedal operation, the driver usually may expect that the brake force can be ultimately generated corresponding to the brake force in the auto-braking mode and the brake force in accordance with the operation of the brake pedal (in the manual braking mode). Therefore, the amount of brake pedal operation may be expected to become smaller compared with the amount of brake pedal operation at a normal state. In this case, the normal state designates a time when the brake pedal is further operated by the driver in a state where the brake force has been already generated by the brake pedal operation by the driver. As a result, the driver may feel uncomfortable when the control mode is switched to the manual braking mode.
Generally known auto-braking controls include a brake force control for maintaining a constant distance with respect to a forwardly located vehicle and brake force control for maintaining a constant vehicle speed while the vehicle is running down-hill. According to the former brake control, the vehicle distance towards the forwardly located vehicle, the speed or acceleration of the forwardly located vehicle, etc. are calculated, for example by a laser or by an image recognizing device. Therefore, a brake hydraulic pressure supplied to a wheel brake cylinder is controlled for maintaining a constant vehicle distance towards the forwardly located vehicle based upon the above-calculated values. According to the latter brake control, a brake hydraulic pressure supplied to a wheel brake cylinder is controlled by operation of a switch by the driver for matching an actual vehicle speed of the vehicle running down-hill with a target vehicle speed.
Known vehicle hydraulic pressure brake apparatus are still susceptible of certain improvements with respect to smoothly switching the control mode from the auto-braking mode to the manual braking mode corresponding to the brake pedal operation when the driver operates the brake pedal during the auto-braking control.
A hydraulic brake apparatus for a vehicle includes a brake operating member, a master cylinder including a master piston which is moved forward in response to a depressing operation of the brake operating member for pressurizing a brake fluid in a reservoir and outputting a master cylinder hydraulic pressure to wheel brake cylinders mounted on respective vehicle wheels in response to the forward movement of the master piston, an auxiliary hydraulic pressure source for pressurizing the brake fluid in the reservoir to a first predetermined pressure level and for outputting a power hydraulic pressure, regulating means connected to the auxiliary hydraulic pressure source and the reservoir for regulating the power hydraulic pressure outputted from the auxiliary hydraulic pressure source to a second predetermined pressure level for driving the master piston by the regulated power hydraulic pressure, and valve means for controlling the power hydraulic pressure supplied from the auxiliary hydraulic pressure source to the regulating means. Control means performs auto-braking control by controlling an operation of the valve means regardless of the depressing operation of the brake operating member for adjusting the master cylinder hydraulic pressure supplied to the wheel brake cylinder, and a braking operation detecting means detects the amount of the depressing operation of the brake operating member. The control means adjusts the master cylinder hydraulic pressure outputted from the master cylinder by adding the master cylinder hydraulic pressure in response to the operation of the brake operating member to a master cylinder hydraulic pressure at the auto-braking control when the brake operating member is operated while the auto-braking control is being performed by the control means.
Preferably, the control means adjusts the master cylinder hydraulic pressure by controlling the operation of the valve means to increase the power hydraulic pressure supplied from the auxiliary hydraulic pressure source to the regulating means corresponding to the amount of the operation of the brake operating member detected by the braking operation detecting means. In addition, vehicle speed detecting means is preferably provided for detecting a vehicle speed, and target vehicle speed determining means is provided for determining a target vehicle speed in response to a vehicle condition. The control means adjusts the master cylinder hydraulic pressure and performs the auto-braking control by controlling the operation of the valve means for meeting the vehicle speed detected by the vehicle speed detecting means during the vehicle running on a down-hill with the target vehicle speed determined by the target vehicle speed determining means. The control means also includes correcting means for correcting the target vehicle speed determined by the target vehicle speed determining means in response to the amount of the depressing operation of the brake operating member detected by the braking operation detecting means in a state where the brake operating member is operated during the auto-braking control. The braking operating detecting means can include a pressure sensor which detects the master cylinder hydraulic pressure outputted from the master cylinder, a depressing force sensor which detects a depressing force applied to the brake operating member, or a stroke sensor which detects a stroke of the brake operating member.
According to another aspect, a vehicle hydraulic brake apparatus includes a brake operating member, a master cylinder including a master piston which is moved forward in response to a depressing operation of the brake operating member to pressurize brake fluid in a reservoir and output a master cylinder hydraulic pressure to a wheel brake cylinder mounted on a vehicle wheel in response to the forward movement of the master piston, an auxiliary hydraulic pressure source for pressurizing the brake fluid in the reservoir to a first predetermined pressure level and outputting a power hydraulic pressure, regulating means connected to the auxiliary hydraulic pressure source and the reservoir for regulating the power hydraulic pressure outputted from the auxiliary hydraulic pressure source to a second predetermined pressure level to drive the master piston, and a solenoid valve unit controlling the power hydraulic pressure supplied from the auxiliary hydraulic pressure source to the regulating means. A sensor detects an amount of operation of the brake operating member, and control means performs auto-braking control by controlling operation of the solenoid valve unit independent of operation of the brake operating member to adjust the master cylinder hydraulic pressure supplied to the wheel brake cylinder. The control means adjusts the master cylinder hydraulic pressure outputted from the master cylinder when the brake operating member is operated while the auto-braking control is being performed by the control means by adding the master cylinder hydraulic pressure produced in response to the amount of operation of the brake operating member to the master cylinder hydraulic pressure produced during the auto-braking control.
Another aspect involves a method of controlling hydraulic pressure produced by a vehicle hydraulic brake apparatus that comprises a brake operating member, a master cylinder which pressurizes brake fluid in a reservoir through movement of a master piston and outputs a master cylinder hydraulic pressure to a wheel brake cylinder mounted on a vehicle wheel in response to the movement of the master piston, an auxiliary hydraulic pressure source which pressurizes the brake fluid in the reservoir to a predetermined pressure level and outputs a power hydraulic pressure to move the master piston, regulating means connected to the auxiliary hydraulic pressure source and the reservoir for regulating the power hydraulic pressure outputted from the auxiliary hydraulic pressure source to a second predetermined pressure level to drive the master piston, and a solenoid valve unit which controls the power hydraulic pressure supplied from the auxiliary hydraulic pressure source to the regulating means. The method involves detecting the amount of operation of the brake operating member, performing auto-braking control independent of operation of the brake operating member by controlling operation of the solenoid valve unit to adjust the master cylinder hydraulic pressure supplied to the wheel brake cylinder, and adjusting the master cylinder hydraulic pressure outputted from the master cylinder when the brake operating member is operated during auto-braking control by adding the master cylinder hydraulic pressure produced in response to the detected amount of operation of the brake operating member to the master cylinder hydraulic pressure produced during the auto-braking control.